The present invention relates to a slide type vacuum pump, and more particularly relates to an improved sealing construction for such a slide type vacuum pump, said pump being for example suitable for being utilized for providing vacuum for a brake booster of an automotive vehicle, which has an improved sealing effect so as to prolong pump life and improve pump efficiency.
The present invention has been described in Japanese patent application Ser. No. Showa 60-176493 (1985), filed by an applicant the same as the entity assigned or owed duty of assignment of the present patent application; and the present patent application hereby incorporates into itself by reference the text of said Japanese Patent Application and the claim and the drawings thereof; a copy is appended to the present application.
There are per se known types of slide type vacuum pumps, such as for example are utilized for providing vacuum for a brake booster of an automotive vehicle. Such a slide type vacuum pump typically has a housing formed with a cylinder bore, with a generally cylindrical piston member being reciprocatingly slidably fitted in said cylinder bore, thus defining a vacuum pumping chamber on one side of said piston member. Typically, to the vacuum pumping chamber there are communicated two check valves, one of which is connected in the orientation appropriate so as to allow air to flow from said vacuum pumping chamber to the outside ambient atmosphere but not in the reverse direction, and the other of which is connected in the opposite orientation so as to allow air to flow from a device which is to be exhausted of air (such as a brake booster of an automobile) into said vacuum pumping chamber but not in the reverse direction. And a mechanical linkage, such as a rocker arm rocked to and fro by resting against an eccentric cam formed on a cam shaft, reciprocatingly slides said piston to and fro in said cylinder bore, so as alternately to increase and diminish the volume of said vacuum pumping chamber so that outward pumping action of air for said device to be exhausted of air is thereby performed.
With a slide type vacuum pump of this configuration, it is very important to provide a good sealing effect between the outer peripheral cylindrical surface of the piston member and the inner cylindrical surface of the cylinder bore, so as to ensure good and durable pumping action. Thus, it is quite typical to provide a seal element such as a seal ring or piston band or the like around said outer peripheral cylindrical surface of said piston member. Such a construction is, for example, disclosed in Japanese Patent Laying Open Publication Ser. No. 59-206685 (1984).
Typically, such a seal element is housed in a circumferential groove provided around the piston member. However, a still unsolved problem of such a construction relates to abrasion wear and deterioration of the seal element. If the seal element becomes worn or deteriorated by heat or the like, the sealing performance provided by said seal element against the cylinder bore may become deteriorated, and this can lead to air leakage and deterioration of vacuum pumping function. Further, there is a possibility that the good sealing of the seal element against the piston, i.e. against the side and bottom of the circumferential groove around the piston in which the seal element is housingly received, should become deteriorated, especially over a long pump service lifetime. Such a problem can also lead to air leakage and deterioration of vacuum pumping function.